• Silicon is a metalloid and has the second
most abundance in earth crust after oxygen,• It is not found in elemental form.• It forms 95 % of the rocks in the earth. • It is found in compounds such as silica,
SiO2, and silicates
• SiO2 is found as sand, quartz and mountain crystals in nature.
Occurrence of Silicon
Preparation
• Heating silica with coke at 3000 0C in electric furnaces.
SiO2(s) + 2C(s) → Si(s) + 2CO(g)
• SiCl4 is heated with H2 or metals.
SiCl4(g) + 2H2(g) → Si(s) + 4HCl(g)
SiCl4(g) + 4Na(s) → Si(s) + 4NaCl(s)
• With strong reducing gents like Cu, Mg and CaCl2.
SiO2(s) + 2Mg(s) → Si(l) + 2MgO(s)
Heat
800oC
600-700oC
Chemical Properties of Silicon
Reactions• React with C, O, S and N at high temperatures (1200 0C)
Si + O2 → SiO2 Si + C → SiC
• Reacts with halogens.
Si(s) + 2F2(g) → SiF4(g) Si(s) + 2Cl2(g) → SiCl4(g)
• React with HF (not other acids)
Si + 4HF → SiF4 + 2H2
• React with hot strong base solutions.
Si + 2KOH + H2O → K2SiO3 + 2H2
Silicon Dioxide, SiO2
• It has similar structure to diamond, 57% of Earth crust is SiO2 and silicates.
•Used to make jeweler, laboratory glassware, various lenses,
ultraviolet light-passing glass, fluorescent lamps, light-sensitive
electrical measurement instruments and glassware.
• It does not dissolve in water or acids (except HF).
SiO2(s) + 4HF(g) → 2H2O(l) + SiF4(g)
• SiO2 is a stable compound. React only strong reducing agents.
SiO2(s) + 2Mg(s) → Si(s) + 2MgO(s)
Silicates
• They are composed of SiO2 and metal oxides Clay:
• Occurs naturally as alumina silicate,
H4Al2SiO9. They can be shaped easily
when they are wet. Used to prepare
pottery, cement, ceramics,
rubber and paint. It is a hard substance,
when cooled it solidifies, without
crystallization and quartz glass is formed.
Glass:
•The main component of glass are sodium silicate,Na2SiO3, and
calcium silicate,CaSiO3. Glass is hard, brittle, amorphous,
transparent, not affected by chemically
active substances. Formula of ordinary
glass, Na2O.CaO.6SiO2.
Cement:
• Main component is calcium aluminosilicate. It is used in
concrete which is mixture of cement, sand, and stone.
Silicones
• Polymeric compounds have properties of both hydrocarbons
and silicon-oxygen compounds.
• They are odorless, colorless, inert
•They are used in hydraulic fluids, enamels, sealing
compounds, varnishes, resins and synthetic rubber.
Uses of Silicon
• In polymers,
solar cells,
different alloys,
cement, glass,
clay, jeweler
industry…etc.